Whenever structural support elements are desired to be rotatable about an axis such that these elements may be moved into any given position relative to each other and to the device to which they are attached, a locking hub is often employed to lock the elements into the desired position.
A typical locking hub device is disclosed in U.S. Pat. No. 4,059,285 to McCoy entitled "Home Shopping Cart" and issued Nov. 22, 1977. This device comprises a first dove-tailed element to be withdrawn from engagement with a second, matingly dove-tailed element, so that the rotational angle between the elements may be adjusted and the assembly resecured.
A modification of the '285 device is described in European Pat. Pub. No. 0 339 890 to Hestair Maclaren Limited entitled "A Frame" and published Nov. 2, 1989. This device comprises a rotatable knob that enables the disengagement and re-engagement of matingly dovetailed elements similar to those of the '285 device.
These and other currently known locking hubs have several disadvantages. First, they are oftentimes unwieldy or difficult to operate. Second, many of the hubs currently known are not reliable in their operation (i.e., the "locked" elements can automatically release when under the forces generated during use). Third, such known hubs do not allow the rotational adjustment of only one articulating member or, if they do, this is accomplished by releasing all of the articulating members and holding those not to be adjusted in position, whilst adjusting the desired member.